1. Field of the Invention
The invention relates to a drive simulator operating method and, more particularly, to a method for operating a drive simulator including a chassis dynamometer system such that a test vehicle thereon can be driven under conditions equivalent to the conditions where the test vehicle is actually driven on a test course.
2. Description of the Prior Art
In conducting various tests on a test vehicle with a gasoline engine, diesel engine, or the like, it is common practice to utilize a drive simulator which normally includes a chassis dynamometer system having therein a direct-current or eddy current dynamometer and a control system for controlling the operation of the drive simulator so that the test vehicle can be driven under conditions equivalent to the conditions where the test vehicle is actually driven on a test course. It is also well known in the art to operate such a drive simulator under the road load control of applying to the dynamometer a road load command expressed by EQU T=A+BV.sup.2 .+-.Wsin.theta.+dv/dt.multidot.W (1)
where A is the rolling resistance, BV.sup.2 is the wind resistance, Wsin.theta. is the acclivity and declivity load, dv/dt.multidot.W is the inertia term, and W is the weight of the vehicle. Such a conventional drive simulator operating method will be described in more detail with reference to FIG. 1 which is a block diagram of a prior art drive simulator. The drive simulator comprises a chassis dynamometer system and a control system. The chassis dynamometer system includes a dynamometer 1 having its rotary drive shaft coupled to a flywheel unit 2 and also to a roller unit 3 on which a test vehicle 4 is placed. The control system includes a torque detector 5 such as including a load cell for detecting the torque of the rotary drive shaft to provide it to one input terminal of a comparator 6, and a speed detector 7 such as including a pulse pick-up associated with the rotary drive shaft for detecting the speed V of the test vehicle. The vehicle speed V is delivered to a first arithmetic circuit 8 where it is converted into the differential of the speed V which in turn is introduced into an inertia term setting circuit 9 having a function of providing an output dv/dt.multidot.W which represents an inertia term value. The vehicle speed V detected by the speed detector 7 is also delivered into a second arithmetic circuit 10 where it is converted into the square of the speed value V which in turn is introduced into a wind resistance setting circuit 11 having a function of providing an output BV.sup.2 which represents a wind resistance value. Designated by the reference numeral 12 is a rolling resistance setting circuit through which the operator manually sets a fixed rolling resistance value A obtained from the design drawing of the test course and designated at 13 is an acclivity/declivity load setting circuit through which the operator manually sets a fixed acclivity/declivity load value Wsin.theta. obtained also from the design drawing of the test course. The outputs from these setting circuits 9, 11, 12 and 13 are introduced into an adder 14 which adds them to provide a road load command value expressed by equation (1) to the other input terminal of the comparator. The comparator 6 compares the road load command value with the rotary drive shaft torque value detected by and delivered from the torque detector 5 to provide a command signal to a dynamometer control circuit 5 which controls the operation of the dynamometer in accordance with the command signal.
One of the difficulties encountered with such a prior art drive simulator operating method is that there is a divergency between simulated conditions and actual vehicle running conditions. This serious difficulty stems mainly from the way to provide the road load command value while disregarding the following factors. First, since it is very difficult to calculate, on the basis of the design drawing of the test course, an acclivity/declivity load command value for all of the ascents and descends existing on the test course, it is normal practice to manually set a fixed acclivity/declivity load command value calculated from values plotted for properly selected ascents and descends. Such an acclivity/declivity load command value cannot correctly correspond to the ascents and descends actually existing on the test course. Second, although a wind resistance command value is selected and set under such an assumption that wind resistance is dependent merely upon test vehicle speed, the wind resistance exerted on the test vehicle is greatly dependent upon the weather condition, particularly upon wind speed and direction. Third, the load exerted on the test vehicle running on a curved road is greatly different from the load exerted on the test vehicle running on a straight road.
Therefore, it will be apparent that the prior art drive simulator operating method where the road load command is determined without regarding many factors such as test course curves and weather conditions and with setting an acclivity/declivity load value in a rough manner cannot provide simulated conditions accurately equivalent to the actual vehicle running conditions.